In computer networks, a network device may be connected to one or more network devices via two or more physical links. The term “link” is often used to refer to the connection between two devices on a network. The link may be a physical medium, such as a copper wire, a coaxial cable, any of a host of different fiber optic lines, or a wireless connection. In addition, network devices may define “virtual” or “logical” links, and map the virtual links to the physical links. In some cases, these two or more links may be logically grouped or aggregated together to form an “aggregated bundle.” For example, one or more routers may be connected to a customer edge device via an aggregate bundle of multiple physical links. In some cases, Ethernet links may be combined into one logical interface for higher bandwidth and redundancy. Ports of the Ethernet links that are combined in this manner are referred to as a link aggregation group (LAG) or bundle.
Generally, link aggregation may improve bandwidth in comparison to that of a single link, while also providing connection redundancy. That is, aggregation of links into logical bundles may result in an available bandwidth of all of the aggregated links combined. In addition, should one of the links of the aggregated bundle fail, the network device may begin sending traffic to the other network device across the non-failed links of the aggregated bundle, thereby providing redundancy in the form of redundant links for delivery of traffic between two devices.
In one example implementation, a customer network site may be given redundant connectivity to a network through multiple provider edge (PE) routers. This form of redundancy is referred to as “multi-homing.” In one type of multi-homing, referred to as “active-standby,” one of the multiple PE routers coupled to the customer network is chosen as the active PE router, or designated forwarder, to send traffic to and from the customer network. The other one or more PE routers are designated as backup forwarders which can be used to send traffic to and from the customer network in the event of a network failure that would preclude the current designated forwarder from sending the traffic. As such, in “active-standby” multi-homed deployments, the standby link is only used when the active link is disabled. In an “active-active” multi-chassis link aggregation group (MC-LAG) configuration, each of the PE routers is configured to actively forward traffic, and the multiple, physical links providing the multi-homed connectivity are logically aggregated and treated as a single, logical link.